Heretofore various devices have been employed for absorbing noise, most of which rely on the acoustical impedance properties of materials for the conversion of sound energy into thermal energy. Typical of these materials are bulk fibers, flow-resistive screens, and absorptive cellular structures. While these prior art materials are highly suitable for many applications, there are certain other applications which preclude their use for reasons related directly to the undesirable characteristics of the sound absorbing materials themselves. Specifically, sound absorbing materials generally have limited structural strength, tend to absorb or wick liquids, and frequently are combustible in nature.
To overcome certain of the shortcomings of the above-described bulk absorbers, specialized "resonant" absorbers have been proposed previously. These type of devices rely on the use of a plurality of closely-spaced tuned chambers or helmholtz resonators to absorb sound. Such arrays of resonators can be strongly absorbent in limited frequency ranges. A principal deterrent to the wide use of these resonant type of absorbers is, however, their high cost of manufacture.
Very often the propagation of sound from a source of noise to a listener or receiver occurs partly or mainly by one or more reflections. In the past it has been customary to attenuate such sound by applying sound absorptive material to the reflecting surfaces. While such attenuation is partially successful, it is obvious that the remainder of the unattenuated sound continues onward towards the receiver.
Accordingly it is a general object of the present invention to dissipate broadband acoustic energy.
It is yet another object of the present invention to dissipate broadband acoustic energy without relying on the use of sound absorbing materials.
It is a further object of the present invention to dissipate broadband acoustic energy without the use of an array of closely spaced tuned resonators.